Laser ‘Knife’

An international research team, led by Federico Capasso at Harvard University and his graduate student Nanfang Yu, recently developed a device that fits to the front of a laser source and tames it into usable beams that are able to travel long distances. So far they can reduce the spread of a beam in one plane by 25 times. This advance can greatly reduce the complexity and cost of optical systems by eliminating the need for the lenses to couple light into optical fibers.

The researchers strapped a 200-micrometer tall metallic structure, dubbed a plasmonic collimator to the front of the laser source. At the top of the device is a horizontal slit just 2 micrometers high which is placed directly over the laser source. It is so narrow that around half the beam passing through is sharply diffracted towards the surface of the metal.The remaining light travels through the slit unimpeded.

As the rest of the beam hits the metal, the high-energy laser light turns into waves of energy rippling through the electrons of the collimator’s surface until they encounter a series of small horizontal grooves that jolt them back into light again. Redirecting the surface plasmons results in very little energy loss and as the distances between the original slit and each groove are chosen to ensure that all the beams emerging from the collimator are synchronized, they come together to form one tightly focused vertical beam.

The result is like a knife blade, sharpened in one direction but extending out in another. The researchers are now working on a version that can sharpen a laser in two dimensions, bringing it to a sharp point like a pencil.